Power transmission lines, which carry electrical power from a power generation plant, are one of the most critical components of an energy generation and transmission system that together forms a power grid. Due to their nature, power transmission lines are susceptible to contact faults, which are the result of an unwanted conduction path that has formed between a conductive surface of the power line and a non-conductive surface, such as a tree. That is, such contact faults are the result of the growth of trees under such power transmission lines, a break in an electrical conductor of the power transmission line, as well as, animal or human contact with the power transmission line. Thus, ensuring the safety and functionality of the power transmission lines of the power grid is a critical concern for its operators.
One type of fault that can impact the power grid is a high-impedance fault. A high-impedance fault (HIF) is typically the result of an electrical contact between a conductor in the power transmission line and a non-conductive surface, which due to the HIF, restricts the fault current below a detectable level of conventional electrical relays. Since high-impedance faults often result in an energized conductor that is in reach of individuals in the public, it poses a tremendous threat or hazard to both the personal safety of such individuals, and to the security of personal property. Such a high impedance fault is difficult to detect because the high impedance fault current appears very similar in magnitude to the small variations of the power network load that are experienced in an energized power grid.
Another safety concern for operators of the power grid relates to the process associated with re-energizing a de-energized power transmission line. This concern is due to the fact that while the power grid is de-energized, there is always a possibility of contact of the power transmission line with humans, animals or trees. While low impedance power line faults can be detected based on the high amount of electrical current passing through the power transmission lines while the power grid/transmission line is energized, the recognition of a fault in a de-energized power grid/transmission line is challenging due to the absence of any electrical current passing through the power transmission line. Thus, in order to monitor the operational status of power transmission lines, including faults associated therewith, several fault detection/transmission line monitoring techniques have been used, including: TDR (time domain reflectometer), FBG (Fiber Bragg Grating), GPS (global positioning sensor) and magnetic based sensors. However, these techniques suffer from various drawbacks, some of which are discussed below.
In one power transmission line monitoring technique, a statistically based fault prediction method is used, whereby data insufficiency, imbalanced data constitution, and threshold settings are used. Their presence in a power distribution fault causes identification problems.
Fault detection in an offline, long-range power line transmission may be achieved via a fault detection method that is based on a time domain reflectometer method (TDR). However, the TDR method is complex, and requires complex hardware.
An optical-based fault current detection method for overhead power transmission lines has also been utilized. This method utilizes a Fiber Bragg Grating (FBG) sensor in order to measure the fault current, while an optical spectrum analyzer is used to monitor the reflected signal. As such, complex hardware is needed to execute this method. In addition, an ice detection sensor, which is based on an FBG strain measurement and a temperature sensor has been proposed, whereby the operation of the ice sensor is dependent on a complex hardware implementation. Thus, such FBG based approaches, again suffer from needing complex hardware.
Another method used to detect power transmission line faults is based on a non-contact magnetic field measurement, which is performed by magnetic sensors. Thus, the location of electrical faults may be identified based on a magnetic field that is measured along the power transmission line. The collected data can be further utilized to identify the fault type and the specific location of the fault within the fault span of the power transmission line. While this method is useful for detecting the high fault current that is produced by a faulty power line, it is not able to be used to predict the possibility of a fault occurrence in the overhead power line based on the power line's health condition.
Alternatively, a method using GPS sensors mounted on the power transmission lines to measure power line sag may be used to monitor powertransmission line health. Such GPS sensors are typically installed on the power line at a midpoint between any two power transmission line supporting towers. Using this method to measure sag in the power line is costly. A monitoring system for the evaluation of the low sag behavior of the overhead conductors in power transmission lines has also been pursued. Such monitoring systems measure power line conductor tension and temperature, as well as wind speed, in order to evaluate the wind load on the conductor of the power transmission line. Another method for measuring power transmission line sag has also been studied, which is based on the electrical current that is inducted on an extra or supplemental resistive line that is installed close to the original power line.
Furthermore, U.S. Pat. No. 6,807,036 teaches a ground fault interrupter that is configured to detect faults in a power transmission line. This interrupter is installed in series between an AC (alternating current) source and the connected power loads. Real-time power transmission line rating techniques based on the collected data from the sensors are presented by U.S. Pat. No. 8,386,198. As such, the conductor of the power transmission line may have a design ampacity that is based upon the design limitations and assumed weather conditions for the conductor's environment, and a dynamic line ampacity that is based upon the received sensor data and the received design limitations of the power transmission line.
Furthermore, since the high-frequency impedance of the power transmission lines of the power grid represents the physical characteristics of the power grid, both the health condition of the power grid and the presence of faults on the power grid can be detected and evaluated by measuring the high-frequency impedance of the power transmission lines of the power grid. However, existing high-frequency impedance measurement devices cannot be directly connected to the energized power grid or network, nor are they capable of measuring the impedance of a specific power transmission line segment.
Therefore, there is a need for a smart sensor network of the present invention that monitors the health condition or status of a power transmission line network of a power grid, and to detect any type of electrical fault in the power transmission line, in real-time. In addition, there is a need for a smart sensor network of the present invention that is capable of monitoring the high-frequency impedance of a power grid to identify the physical characteristics of the power grid, so as to monitor and evaluate both its health condition and the presence of electrical faults, in real-time. Furthermore, there is a need for a smart sensor network of the present invention that utilizes the detection of a high-frequency impedance fault to predict the health condition of an electrical fault occurrence on power transmission lines. Additionally, there is a need for a smart sensor network of the present invention that is configured to monitor the health condition of a power transmission system or power grid, which includes overhead, underground, or home/residential power transmission lines in real-time, as well as to monitor a power system of a DC railway system, whereby the present invention monitors the impedance of a desired power line segment in real-time. There is also a need for a smart sensor system of the present invention that can be coupled to a power transmission line, through magnetic coupling, including magnetic field coupling or inductive coupling.